Soft Ferrite Magnet

Ferrites that are used intransformerorelectromagneticcorescontainnickel,zinc, and/ormanganesecompounds. They have a lowcoercivityand are calledsoft ferrites. The low coercivity means the material'smagnetizationcan easily reverse direction without dissipating much energy (hysteresis losses), while the material's highresistivitypreventseddy currentsin the core, another source of energy loss. Because of their comparatively low losses at high frequencies, they are extensively used in the cores ofRFtransformers andinductorsin applications such asswitched-mode power suppliesandloopstick antennasused in AM radios.

The most common soft ferrites are:

Manganese-zinc ferrite(MnZn, with the formulaMnaZn(1-a)Fe2O4). MnZn have higherpermeabilityandsaturation inductionthan NiZn.

Nickel-zinc ferrite(NiZn, with the formulaNiaZn(1-a)Fe2O4). NiZn ferrites exhibit higher resistivity than MnZn, and are therefore more suitable for frequencies above 1 MHz.

For applications below 5 MHz, MnZn ferrites are used; above that, NiZn is the usual choice. The exception is withcommon mode inductors, where the threshold of choice is at 70 MHz.